1. Field of the Invention
The invention is in the field of capsules and encapsulation and relates to an improved process for encapsulating materials, especially biological materials such as living tissue, cells, or bacteria, wherein the materials remain viable and/or in a protected state within a membrane selectivity permeable to nutrients and to the metabolic products of the biological materials. Many other applications are seen, such as injectable capsules providing for the slow release of drugs, for example.
2. Description of the Related Art
The capsules of this invention are related to those art capsules resulting from interfacial reaction between polycations and polyanions.
Lim in U.S. Pat. No. 4,352,883 teaches a two-stage encapsulation of various biological materials wherein, in the main, droplets of an aqueous solution containing, for example, cationic sodium alginate and suspended active materials are introduced into a solution of a counter ion such as Ca++ in the form of the chloride, whereby to precipitate calcium alginate gel as a solid sphere incorporating the active material. Thereafter, the spheres are transferred to a solution of a polyanion such as polylysine, thus precipitating an organic anion-cation membrane around the sphere. Gel in the interior of the capsules is reliquified by immersing the spheres in a mixture of saline solution and citrate buffer of pH 7.4.
Rha and Rodriguez-Sanchez in European patent application No. 85101490 teach the direct formation of capsules having a liquid core by the process of mixing active material with one of two solutions, one solution containing an anionic polymer, the other a cationic polymer. The mixture containing the active material is then added dropwise to the other solution. The permeability of the membrane formed in this manner is controlled, according to patentees, by adjusting the concentration of the cationic and anionic polymers, the pH, the presence or absence of polyvalent counter ions, e.g. Ca++ or Ba++ or phospate as appropriate, the molecular weight of the polymers as well as through selection of the polymers themselves. Sodium alginate and chitosan, inter alia, are taught as anionic and cationic polymers, respectively.
Knorr et al in Food Technology, 39,(10): 135-142, 1985 reviewed the field, and references therein are incorporated by reference.